| Contraction in a muscle cell is produced by an [[Action_potential|action potential ]]travelling along a motor neurone and arriving at a [[synapse]]. The voltage gradient causes voltage-gated calcium [[Ion_channels|ion channels]] in the [[presynaptic|presynaptic ]]neurone to open, triggering [[Vesicles|vesicles]] containing [[Neurotransmitter|neurotransmitters]], specifically acetylcholine, to travel towards the [[sarcolemma|sarcolemma]]; fusing with the membrane and releasing acetylcholine into the [[synaptic cleft|synaptic cleft ]]<ref name="null">Bowness E, Braid K, Brazier J, Burrows C, Craig K, Gillham R, Towle J. (2009), A2-level Biology The Revision Guide Exam Board AQA, page 57, Newcastle-upon-Tyne: CGP books.</ref>. They diffuse across the cleft where they bind to specific [[Receptor|receptors]] called nicotinic cholinergic receptors, on the sarcolemma, where the [[depolarisation|depolarisation]] travels along the membrane and deep into the cell via [[T-tubules|T-tubules ]]<ref name="null">Bowness E, Braid K, Brazier J, Burrows C, Craig K, Gillham R, Towle J. (2009), A2-level Biology The Revision Guide Exam Board AQA, page 58 -60, Newcastle-upon-Tyne: CGP books.</ref>. Therefore it allows the [[sarcoplasmic reticulum|sarcoplasmic reticulum]] to become depolarised, releasing calcium ions and triggering muscle contraction to take place by the [[The_Sliding_Filament_Theory|sliding filament theory ]]<ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008), Molecular Biology of The Cell, page 1028-1029, 5th edition, New York:Garland Science.</ref>.
| | See [[Smooth Muscle|Smooth Muscle]] |